Method of forming silicon-containing film

ABSTRACT

A method of forming a silicon-containing film includes: an adsorption step of supplying a silicon-containing gas represented by a general formula XSiCl3 (wherein X is an element whose bonding energy with Si is smaller than bonding energy of a Si—Cl bond) into a processing chamber accommodating substrates to cause the silicon-containing gas to be adsorbed to a surface of each of the substrates; and a reaction step of supplying a reaction gas reacting with the silicon-containing gas into the processing chamber to cause the silicon-containing gas adsorbed to the surface of each of the substrates to react with the reaction gas.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Continuation Application of U.S. patent application Ser. No.15/820,489, filed Nov. 22, 2017, an application claiming the benefit ofpriority from Japanese Patent Application No. 2016-227761 filed on Nov.24, 2016 and Japanese Patent Application No. 2017-114590, filed on Jun.9, 2017, the contents of which are incorporated by reference in theirentirety.

TECHNICAL FIELD

The present disclosure relates to a method of forming asilicon-containing film.

BACKGROUND

In the related art, there is known a method of forming a silicon nitridefilm on a semiconductor wafer by using an ALD (Atomic Layer Deposition)method in which an adsorption step and a nitriding step are repeated.

In the case of forming a silicon nitride film on a semiconductor waferby using an ALD method, the film formation time is shortened and theproductivity is improved, for example, by a method of increasing aprocess temperature to enhance the adsorption efficiency of a rawmaterial gas or a method of shortening the time of one cycle.

However, in the method of increasing the process temperature, uniformitymay deteriorate due to a CVD reaction. In the method of shortening thetime of one cycle, the reaction time per cycle is shortened. Therefore,the adsorption reaction and the nitriding reaction may becomeinsufficient and the film quality may deteriorate. Thus, in the methodof related art, it was difficult to achieve both the enhancement inproductivity and the improvement in film quality.

SUMMARY

Some embodiments of the present disclosure provide a method of forming asilicon-containing film, which is capable of achieving both theenhancement in productivity and the improvement in film quality.

According to one embodiment of the present disclosure, there is provideda method of forming a silicon-containing film including: an adsorptionstep of supplying a silicon-containing gas represented by a generalformula XSiCl₃ (wherein X is an element whose bonding energy with Si issmaller than bonding energy of a Si—Cl bond) into a processing chamberaccommodating substrates to cause the silicon-containing gas to beadsorbed to a surface of each of the substrates; and a reaction step ofsupplying a reaction gas reacting with the silicon-containing gas intothe processing chamber to cause the silicon-containing gas adsorbed tothe surface of each of the substrates to react with the reaction gas.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the presentdisclosure, and together with the general description given above andthe detailed description of the embodiments given below, serve toexplain the principles of the present disclosure.

FIG. 1 is a schematic sectional view of a film forming apparatussuitable for carrying out a method of forming a silicon nitride filmaccording to an embodiment of the present disclosure.

FIG. 2 is a schematic perspective view of the film forming apparatusshown in FIG. 1.

FIG. 3 is a schematic plan view showing a configuration inside a vacuumcontainer of the film forming apparatus shown in FIG. 1.

FIG. 4 is a schematic sectional view of the vacuum container taken alonga concentric circle of a rotary table of the film forming apparatusshown FIG. 1.

FIG. 5 is another schematic sectional view of the film forming apparatusshown in FIG. 1.

FIG. 6 is a flowchart showing a method of forming a silicon nitride filmaccording to an embodiment of the present disclosure.

FIG. 7 is a diagram showing the cycle time dependency of a depositionrate of a silicon nitride film.

FIG. 8 is a diagram showing the leakage current characteristics of asilicon nitride film.

FIG. 9 is a diagram showing the relationship between the temperature ofa wafer and the loading effect.

FIG. 10 is a schematic view of another example of a film formingapparatus suitable for carrying out a method of forming a siliconnitride film according to an embodiment of the present disclosure.

FIG. 11 is a schematic view of another example of a film formingapparatus suitable for carrying out a method of forming a siliconnitride film according to an embodiment of the present disclosure.

FIG. 12 is a diagram for explaining a method of forming a siliconnitride film according to a second embodiment.

FIG. 13 is a diagram showing the relationship between the temperature ofa wafer and the cycle rate of a silicon nitride film.

FIG. 14 is a diagram showing the relationship between the temperature ofa wafer and the in-plane uniformity of a film thickness of a siliconnitride film.

FIG. 15 is a diagram showing the relationship between the temperature ofa wafer and the incubation cycle.

FIG. 16 is a diagram for explaining the bonding energy.

FIGS. 17A and 17B are views for explaining an adsorption mechanism of asilicon-containing gas.

FIG. 18 is a view showing an example of a three-dimensional NAND flashmemory with a SONOS structure.

DETAILED DESCRIPTION

Hereinafter, a mode for carrying out the present disclosure will bedescribed with reference to the drawings. In the specification and thedrawings, substantially the same components are denoted by the samereference numerals, and redundant description is omitted. Reference willnow be made in detail to various embodiments, examples of which areillustrated in the accompanying drawings. In the following detaileddescription, numerous specific details are set forth in order to providea thorough understanding of the present disclosure. However, it will beapparent to one of ordinary skill in the art that the present disclosuremay be practiced without these specific details. In other instances,well-known methods, procedures, systems, and components have not beendescribed in detail so as not to unnecessarily obscure aspects of thevarious embodiments.

First Embodiment

In the first embodiment, as an example of a method of forming asilicon-containing film of the present disclosure, a case of forming asilicon nitride film using a semi-batch type film forming apparatus thatperforms a film forming process collectively on a plurality of wafersmounted on a rotary table will be described.

Film Forming Apparatus

First, a film forming apparatus suitable for carrying out a method offorming a silicon nitride film according to an embodiment of the presentdisclosure will be described. FIG. 1 is a schematic sectional view of afilm forming apparatus suitable for carrying out a method of forming asilicon nitride film according to an embodiment of the presentdisclosure. FIG. 2 is a schematic perspective view of the film formingapparatus shown in FIG. 1. FIG. 3 is a schematic plan view showing aconfiguration inside a vacuum container of the film forming apparatusshown in FIG. 1.

Referring to FIGS. 1 to 3, the film forming apparatus includes a flatvacuum container 1 having a substantially circular plan-view shape, anda rotary table 2 provided inside the vacuum container 1 and having arotation center at the center of the vacuum container 1. The vacuumcontainer 1 includes a container body 12 having a bottomed cylindricalshape, and a top plate 11 airtightly and removably arranged on the uppersurface of the container body 12 via a seal member 13 (FIG. 1) such as,for example, an O ring or the like.

The rotary table 2 is fixed to a cylindrical core portion 21 at thecenter portion thereof. The core portion 21 is fixed to the upper end ofa rotating shaft 22 extending in the vertical direction. The rotatingshaft 22 passes through a bottom portion 14 of the vacuum container 1.The lower end of the rotating shaft 22 is attached to a driving part 23that rotates the rotating shaft 22 (FIG. 1) about a vertical axis. Therotating shaft 22 and the driving part 23 are accommodated in a tubularcase body 20 whose top surface is opened. A flange portion provided onthe upper surface of the case body 20 is airtightly attached to thelower surface of the bottom portion 14 of the vacuum container 1,whereby the airtight state between the internal atmosphere of the casebody 20 and the external atmosphere is maintained.

On the surface portion of the rotary table 2, as shown in FIGS. 2 and 3,circular recesses 24 capable of mounting a plurality of (five, in theillustrated example) semiconductor wafers (hereinafter referred to as“wafer W”) as substrates are provided along the rotation direction(circumferential direction). In FIG. 3, for the sake of convenience, thewafer W is shown to be mounted only in one recess 24. The recess 24 hasan inner diameter slightly, for example, 4 mm larger than the diameterof the wafer W and a depth substantially equal to the thickness of thewafer W. Therefore, when the wafer W is accommodated in the recess 24,the surface of the wafer W and the surface of the rotary table 2 (thearea where the wafer W is not mounted) have the same height. Throughholes (not shown) through which, for example, three lift pins forsupporting the back surface of the wafer W and moving the wafer W up anddown are penetrated are formed on the bottom surface of the recess 24.

FIGS. 2 and 3 are views for explaining the structure inside the vacuumcontainer 1. The illustration of the top plate 11 is omitted for theconvenience of explanation. As shown in FIGS. 2 and 3, above the rotarytable 2, reaction gas nozzles 31 and 32 and separation gas nozzles 41and 42 made of, for example, quartz are arranged so as to be spacedapart from one another in the circumferential direction of the vacuumcontainer 1 (the rotation direction of the rotary table 2 indicated byan arrow A in FIG. 3). In the illustrated example, the separation gasnozzle 41, the reaction gas nozzle 31, the separation gas nozzle 42, andthe reaction gas nozzle 32 are arranged in the named order in theclockwise direction (the rotation direction of the rotary table 2) froma transfer port 15 described later. These nozzles 31, 32, 41, and 42 areintroduced into the vacuum container 1 from the outer peripheral wall ofthe vacuum container 1 by fixing the gas introduction ports 31 a, 32 a,41 a, and 42 a (FIG. 3), which are the base end portions of the nozzles31, 32, 41, and 42, to the outer peripheral wall of the container body12. The nozzles 31, 32, 41, and 42 are attached so as to extendhorizontally with respect to the rotary table 2 along the radialdirection of the container body 12.

The reaction gas nozzle 31 is connected to a silicon-containing gassupply source (not shown) via a pipe (not shown), a flow rate controller(not shown) and the like. The reaction gas nozzle 32 is connected to anitrogen-containing gas supply source (not shown) via a pipe (notshown), a flow rate controller (not shown) and the like. Both of theseparation gas nozzles 41 and 42 are connected to a separation gassupply source (not shown) via a pipe (not shown), a flow rate controlvalve (not shown) and the like. As a separation gas, a rare gas such asa helium (He) gas, an argon (Ar) gas or the like, or an inert gas suchas a nitrogen (N₂) gas or the like may be used. In the presentembodiment, the N₂ gas is used.

In the reaction gas nozzles 31 and 32, a plurality of gas dischargeholes 35 opened toward the rotary table 2 are arranged at intervals of,for example, 10 mm, along the length direction of the reaction gasnozzles 31 and 32. The region under the reaction gas nozzle 31 is afirst processing region P1 for causing a silicon-containing gas to beadsorbed to the wafer W. The region under the reaction gas nozzle 32 isa second processing region P2 for nitriding the silicon-containing gasadsorbed to the wafer W in the first processing region P1.

Referring to FIGS. 2 and 3, in the vacuum container 1, two convexportions 4 are provided. In order to define separation regions Dtogether with the separation gas nozzles 41 and 42, the convex portions4 are attached to the back surface of the top plate 11 so as to protrudetoward the rotary table 2 as described later. Furthermore, the convexportion 4 has a fan-like plan-view shape with the vertex portion thereofcut in a circular arc shape. In the present embodiment, the innercircular arc of the convex portion 4 is connected to a protrusionportion 5 (described later), and the outer circular arc of the convexportion 4 is disposed so as to extend along the inner peripheral surfaceof the container body 12 of the vacuum container 1.

FIG. 4 shows a cross section of the vacuum container 1 taken along theconcentric circle of the rotary table 2 from the reaction gas nozzle 31to the reaction gas nozzle 32. As shown in FIG. 4, the convex portion 4is attached to the back surface of the top plate 11. Therefore, a flatlow ceiling surface 44 (first ceiling surface), which is the lowersurface of the convex portion 4, and a ceiling surface 45 (a secondceiling surface), which is located on both sides of the ceiling surface44 in the circumferential direction and which is higher than the ceilingsurface 44, are present inside the vacuum container 1. The ceilingsurface 44 has a fan-like plan-view shape with the vertex thereof cut ina circular arc shape. As shown in FIG. 4, a groove portion 43 formed soas to extend in the radial direction is formed in the convex portion 4at the circumferential center thereof. The separation gas nozzle 42 isaccommodated in the groove portion 43. Similarly, a groove portion 43 isformed in another convex portion 4. The separation gas nozzle 41 isaccommodated in the groove portion 43. In addition, the reaction gasnozzles 31 and 32 are respectively provided in the spaces under the highceiling surface 45. These reaction gas nozzles 31 and 32 are spacedapart from the ceiling surface 45 and are provided in the vicinity ofthe wafer W. As shown in FIG. 4, the reaction gas nozzle 31 is providedin the right space 48 under the high ceiling surface 45, and thereaction gas nozzle 32 is provided in the left space 49 under the highceiling surface 45.

In the separation gas nozzles 41 and 42 accommodated in the grooveportions 43 of the convex portions 4, a plurality of gas discharge holes41 h (see FIG. 4) opened toward the rotary table 2 are arranged alongthe length direction of the separation gas nozzles 41 and 42 atintervals of, for example, 10 mm.

The ceiling surface 44 defines a separation space H, which is a narrowspace, with respect to the rotary table 2. When an N₂ gas is suppliedfrom the discharge holes 42 h of the separation gas nozzle 42, the N₂gas flows toward the space 48 and the space 49 through the separationspace H. At this time, the pressure of the separation space H may bemade higher than the pressures of the spaces 48 and 49 by the N₂ gasbecause the volume of the separation space H is smaller than the volumesof the spaces 48 and 49. That is to say, a high-pressure separationspace H is formed between the spaces 48 and 49. The N₂ gas flowing outfrom the separation space H into the spaces 48 and 49 acts as acounter-flow against the silicon-containing gas from the firstprocessing region P1 and the nitrogen-containing gas from the secondprocessing region P2. Therefore, the silicon-containing gas from thefirst processing region P1 and the nitrogen-containing gas from thesecond processing region P2 are separated by the separation space H.Accordingly, the silicon-containing gas and the nitrogen-containing gasare prevented from mixing and reacting in the vacuum container 1.

In consideration of the pressure in the vacuum container 1, the rotationspeed of the rotary table 2, the supply amount of the separation gas (N₂gas) to be supplied, and the like during film formation, the height hlof the ceiling surface 44 with respect to the upper surface of therotary table 2 may be set to a height suitable for making the pressurein the separation space H higher than the pressures in the spaces 48 and49.

The protrusion portion 5 (FIGS. 2 and 3) surrounding the outer peripheryof the core portion 21 for fixing the rotary table 2 is provided on thelower surface of the top plate 11. In the present embodiment, theprotrusion portion 5 is continuous with the portions on the rotationcenter side of the convex portions 4. The lower surface of theprotrusion portion 5 is formed at the same height as the ceiling surface44.

FIG. 1 referred to above is a sectional view taken along line I-I′ inFIG. 3 and shows a region where the ceiling surface 45 is provided. Onthe other hand, FIG. 5 is a sectional view showing a region where theceiling surface 44 is provided. As shown in FIG. 5, in the peripheraledge portion (the portion on the outer edge side of the vacuum container1) of the fan-shaped convex portion 4, there is formed a bent portion 46that bends in an L shape so as to face the outer end surface of therotary table 2. Similar to the convex portion 4, the bent portion 46suppresses the entry of the reaction gases from both sides of theseparation region D and suppresses the mixing of both reaction gases.Since the fan-shaped convex portion 4 is provided on the top plate 11and the top plate 11 can be removed from the container body 12, a slightgap exists between the outer peripheral surface of the bent portion 46and the container body 12. The gap between the inner peripheral surfaceof the bent portion 46 and the outer end surface of the rotary table 2and the gap between the outer peripheral surface of the bent portion 46and the container body 12 are set to be the same as the height of theceiling surface 44 with respect to the upper surface of the rotary table2.

In the separation region D, the inner peripheral wall of the containerbody 12 is formed as a vertical surface close to the outer peripheralsurface of the bent portion 46 as shown in FIG. 4. On the other hand, inthe portion other than the separation region D, as shown in FIG. 1, theinner peripheral wall of the container body 12 is recessed outward, forexample, from the portion facing the outer end surface of the rotarytable 2 throughout the bottom portion 14. Hereinafter, for theconvenience of description, the recessed portion having a substantiallyrectangular cross-sectional shape will be referred to as an exhaustregion. More specifically, the exhaust region communicating with thefirst processing region P1 will be referred to as a first exhaust regionE1, and the region communicating with the second processing region P2will be referred to as a second exhaust region E2. As shown in FIGS. 1to 3, a first exhaust port 61 and a second exhaust port 62 are formed inthe bottom portions of the first exhaust region E1 and the secondexhaust region E2, respectively. As shown in FIG. 1, each of the firstexhaust port 61 and the second exhaust port 62 is connected to a vacuumexhaust means, for example, a vacuum pump 64 through an exhaust pipe 63.A pressure controller 65 is provided between the vacuum pump 64 and theexhaust pipe 63.

As shown in FIGS. 1 and 5, a heater unit 7 serving as a heating means isprovided in the space between the rotary table 2 and the bottom portion14 of the vacuum container 1. The wafer W on the rotary table 2 isheated to a temperature determined by a process recipe. On the lowerside in the vicinity of the peripheral edge of the rotary table 2, aring-shaped cover member 71 is provided (FIG. 5) in order to partitionthe atmosphere in a region extending from the upper space of the rotarytable 2 to the first exhaust region E1 and the second exhaust region E2and the atmosphere where the heater unit 7 is placed and to prevent agas from entering the lower region of the rotary table 2. The covermember 71 includes an inner member 71 a provided so that the innermember 71 a faces the outer edge portion of the rotary table 2 and theouter peripheral side of the outer edge portion of the rotary table 2from below, and an outer member 71 b provided between the inner member71 a and the inner wall surface of the vacuum container 1. The outermember 71 b is provided close to the bent portion 46 below the bentportion 46 formed in the outer edge portion of the convex portion 4 inthe separation region D. The inner member 71 a surrounds the entirecircumference of the heater unit 7 below the outer edge portion of therotary table 2 (and below the portion slightly outside the outer edgeportion).

The bottom portion 14 closer to the rotation center than the space wherethe heater unit 7 is disposed protrudes upward so as to approach thecore portion 21 in the vicinity of the center portion of the lowersurface of the rotary table 2, thereby forming a projection portion 12a. A narrow space is formed between the projection portion 12 a and thecore portion 21. Furthermore, a narrow gap is formed between the innercircumferential surface of the through hole of the rotating shaft 22passing through the bottom portion 14 and the rotating shaft 22. Thesespaces communicate with the case body 20. A purge gas supply pipe 72 forsupplying an N₂ gas, which is a purge gas, into the narrow spaces andpurging the narrow spaces is provided in the case body 20. A pluralityof purge gas supply pipes 73 for purging the arrangement space of theheater unit 7 is provided in the bottom portion 14 of the vacuumcontainer 1 at predetermined angular intervals in the circumferentialdirection under the heater unit 7 (one purge gas supply pipe 73 is shownin FIG. 5). In order to suppress the entry of a gas into the regionwhere the heater unit 7 is provided, a lid member 7 a that covers a gapbetween the inner wall surface of the outer member 71 b (the uppersurface of the inner member 71 a) and the upper end portion of theprojection portion 12 a in the circumferential direction is providedbetween the heater unit 7 and the rotary table 2. The lid member 7 a maybe made of quartz, for example.

In addition, a separation gas supply pipe 51 is connected to the centralportion of the top plate 11 of the vacuum container 1 and is configuredto supply an N₂ gas, which is a separation gas, to a space 52 betweenthe top plate 11 and the core portion 21. The separation gas supplied tothe space 52 is discharged toward the peripheral edge along the wafermounting region side surface of the rotary table 2 via a narrow space 50between the protrusion portion 5 and the rotary table 2. The space 50may be maintained at a higher pressure than the space 48 and the space49 by the separation gas. Therefore, the space 50 suppresses thesilicon-containing gas supplied to the first processing region P1 andthe nitrogen-containing gas supplied to the second processing region P2from passing through the central region C and being mixed each other. Inother words, the space 50 (or the central region C) may function justlike the separation space H (or the separation region D).

As shown in FIGS. 2 and 3, on the side wall of the vacuum container 1,there is formed the transfer port 15 for delivering a wafer W, which isa substrate, between an external transfer arm 10 and the rotary table 2.The transfer port 15 is opened and closed by a gate valve (not shown).In the recess 24 which is the wafer mounting region of the rotary table2, the wafer W is delivered to and from the transfer arm 10 at aposition facing the transfer port 15. Therefore, in a regioncorresponding to the delivery position on the lower side of the rotarytable 2, there are provided delivery-purpose lift pins (not shown)penetrating the recess 24 to lift the wafer W from the back surfacethereof and a lift mechanism (not shown) for the lift pins.

As shown in FIG. 1, the film forming apparatus according to the presentembodiment includes a control part 100 formed of a computer forcontrolling the overall operation of the apparatus. In the memory of thecontrol part 100, there is stored a program for causing the film formingapparatus to execute the method of forming a silicon nitride filmdescribed below under the control of the control part 100. In theprogram, step groups are incorporated so as to execute the method offorming a silicon nitride film described later. The program is stored ina medium 102 such as a hard disk, a compact disk, a magneto-opticaldisk, a memory card, a flexible disk or the like. The program is readinto a memory part 101 by a predetermined reading device and isinstalled in the control part 100.

(Method of Forming Silicon Nitride Film)

Next, a method of forming a silicon nitride film according to anembodiment of the present disclosure will be described. The method offorming a silicon nitride film according to the embodiment of thepresent disclosure is a method of forming a silicon nitride film on thesurface of a wafer W by using an ALD (Atomic Layer Deposition) method inwhich an adsorption step and a nitriding step are repeated. Theadsorption step is a step in which a silicon-containing gas representedby a general formula XSiCl₃ (wherein X is an element whose bondingenergy with Si is smaller than that of a Si—Cl bond) is supplied intothe vacuum container 1 accommodating the wafer W to cause thesilicon-containing gas to be adsorbed to the surface of the wafer W. Asthe silicon-containing gas, any gas may be used as long as it isrepresented by the general formula XSiCl₃ (wherein X is an element whosebonding energy with Si is smaller than that of a Si—Cl bond). Examplesof the silicon-containing gas include trichlorosilane (HSiCl₃), BrSiCl₃and ISiCl₃. The nitriding step is a step in which a nitrogen-containinggas is supplied into the vacuum container 1 to deposit an atomic layeror a molecular layer of a reaction product of the silicon-containing gasand the nitrogen-containing gas.

Hereinafter, a case where the above-described film forming apparatus isused will be described as an example with reference to FIG. 6. Themethod of forming a silicon nitride film according to the embodiment ofthe present disclosure may be carried out by using another film formingapparatus. FIG. 6 is a flowchart showing the method of forming a siliconnitride film according to the embodiment of the present disclosure.

First, in step S1, the wafer W is mounted on the rotary table 2.Specifically, a gate valve (not shown) is opened, and the wafer W isdelivered from the outside to the recess 24 of the rotary table 2 viathe transfer port 15 (FIGS. 2 and 3) by the transfer arm 10 (FIG. 3).The delivery of the wafer W is performed by raising and lowering thelift pins (not shown) from the bottom side of the vacuum container 1 viathe through holes of the bottom surface of the recess 24 when the recess24 is stopped at a position facing the transfer port 15. Such deliveryof the wafer W is performed by intermittently rotating the rotary table2 so that the wafer W is mounted in each of the five recesses 24 of therotary table 2.

Subsequently, the gate valve is closed, and the interior of the vacuumcontainer 1 is evacuated to a reachable degree of vacuum by the vacuumpump 64. Thereafter, in step S2, an N₂ gas is supplied from theseparation gas nozzles 41 and 42 at a predetermined flow rate. An N₂ gasis also supplied from the separation gas supply pipe 51 and the purgegas supply pipes 72 and 73 at a predetermined flow rate. Along withthis, the interior of the vacuum container 1 is controlled to be apreset processing pressure by the pressure controller 65 (FIG. 1). Next,the wafer W is heated to a predetermined temperature (for example, 400degrees C. to 850 degrees C.) by the heater unit 7 while rotating therotary table 2 clockwise, for example, at a rotation speed of 20 rpm.

Thereafter, in step S3, a silicon-containing gas represented by ageneral formula XSiCl₃ (wherein X is an element whose bonding energywith Si is smaller than that of a Si—Cl bond) is supplied from thereaction gas nozzle 31 (FIGS. 2 and 3), and a nitrogen-containing gas(for example, ammonia (NH₃)) is supplied from the reaction gas nozzle32. By the rotation of the rotary table 2, the wafer W passes throughthe first processing region P1, the separation region D (separationspace H), the second processing region P2, and the separation region D(separation space H) in the named order (FIG. 3). First, in the firstprocessing region P1, the silicon-containing gas from the reaction gasnozzle 31 is adsorbed to the wafer W (adsorption step). Next, when thewafer W reaches the second processing region P₂ through the separationspace H (separation region D) kept in an N₂ gas atmosphere, thesilicon-containing gas adsorbed to the wafer W reacts with thenitrogen-containing gas supplied from the reaction gas nozzle 32,whereby a silicon nitride film is formed on the wafer W (nitridingstep). Then, the wafer W reaches the separation region D (the separationspace H kept in the N₂ gas atmosphere). The rotary table 2 is rotated apredetermined number of times, and the cycle is repeated a plurality oftimes. In this way, in step S3, the silicon-containing gas and thenitrogen-containing gas are alternately supplied to the surface of thewafer W.

In the meantime, it is determined whether or not the silicon-containinggas from the reaction gas nozzle 31 and the nitrogen-containing gas fromthe reaction gas nozzle 32 have been supplied for a predetermined time(step S4). The predetermined time is set depending on the target filmthickness of the silicon nitride film to be formed on the surface of thewafer W. If the target film thickness is determined, the time of thestep of forming the silicon nitride film may be appropriately determinedin consideration of the conditions such as the rotation speed of therotary table 2, the flow rates of the silicon-containing gas and thenitrogen-containing gas, the wafer temperature and the like.

If it is determined in step S4 that the predetermined time has notelapsed, the process returns to step S3 to continue the silicon nitridefilm forming process (the adsorption step and nitriding step). On theother hand, if the predetermined time has elapsed, the supply of thesilicon-containing gas and the nitrogen-containing gas is stopped toterminate the film formation.

As described above, in the method of forming a silicon nitride filmaccording to the embodiment of the present disclosure, in the adsorptionstep, the silicon-containing gas represented by the general formulaXSiCl₃ (wherein X is an element whose bonding energy with Si is smallerthan that of a Si—Cl bond) is supplied to cause the silicon-containinggas to be adsorbed to the surface of the wafer W. Accordingly, when theSi-containing gas is adsorbed to the surface of the wafer W, a Si—X bondis broken because the Si—X bond in XSiCl₃ is weaker than a Si—Cl bond.That is to say, three functional groups become chloro groups (Cl—).Therefore, the surface to which the silicon-containing gas is adsorbedhas a structure in which the electron density on a silicon atom (Si)decreases and the silicon atom (Si) is likely to make a bond with anitrogen atom (N) in an electrophilic manner. Thus, the surface iseasily nitrided by the nitrogen-containing gas such as NH₃ or the like.As a result, in the nitriding step performed after the adsorption step,the reaction rate of the silicon-containing gas and thenitrogen-containing gas is improved and the productivity is enhanced. Inaddition, the three-dimensional structure of SiN is easily formed.Therefore, the film quality is improved.

In addition, the unreacted bonding sites on the surface of the wafer Ware reduced by increasing the adsorption rate and the nitriding rate.Therefore, the variation in deposition rate is reduced in the plane ofthe wafer W, whereby the in-plane uniformity is improved.

Furthermore, since the three-dimensional structure of SiN is easilyformed, the film grows like a tree. As a result, the reaction surface onwhich the adsorption of the silicon-containing gas and the nitriding ofthe silicon-containing gas are performed is enlarged. Thus, the time(incubation time) until the film begins to grow on the surface of thewafer W is shortened.

Example

Next, an Example and a Comparative Example conducted to confirm theeffect of the silicon nitride film will be described. In the Example andthe Comparative Example, silicon nitride films were formed under thefollowing process conditions. In addition, the characteristics of thesilicon nitride films formed in the Example and the Comparative Examplewere evaluated.

Example

-   -   Silicon-containing gas: trichlorosilane (HSiCl₃) (hereinafter        also referred to as “TrCS”)    -   Nitrogen-containing gas: ammonia (NH₃)    -   Pressure: 4.0 Torr (533 Pa)    -   Wafer temperature: 760 degrees C.    -   Rotation speed of rotary table: 2 rpm, 5 rpm, 10 rpm, 30 rpm,        and 60 rpm

Comparative Example

-   -   Silicon-containing gas: dichlorosilane (H₂SiCl₂) (hereinafter        also referred to as “DCS”)    -   Nitrogen-containing gas: ammonia (NH₃)    -   Pressure: 4.0 Torr (533 Pa)    -   Wafer temperature: 760 degrees C.    -   Rotation speed of rotary table 2: 2 rpm, 10 rpm, and 30 rpm

FIG. 7 is a diagram showing the cycle time dependency of the depositionrate of the silicon nitride film. In FIG. 7, the horizontal axisrepresents the cycle time [sec] and the rotation speed [rpm], and thevertical axis represents the cycle rate [nm/cycle]. The cycle timerefers to the time during which the rotary table 2 makes one revolution.The rotation speed refers to the rotation speed of the rotary table 2.The cycle rate refers to the thickness of a film formed while the rotarytable 2 makes one revolution. In FIG. 7, the cycle rate of the siliconnitride film (Example) in the case of using TrCS as thesilicon-containing gas is indicated by a characteristic line α, and thecycle rate of the silicon nitride film (Comparative Example) in the caseof using DCS as the silicon-containing gas is indicated by acharacteristic line β.

As shown in FIG. 7, when TrCS indicated by the characteristic line α isused, the cycle rate is hardly changed even if the cycle time isincreased. From this result, it is considered that the silicon nitridefilm is formed by the deposition of each atomic layer attributable to anALD reaction without thermal decomposition of TrCS.

On the other hand, in the case of using DCS indicated by thecharacteristic line β, if the cycle time is lengthened, the cycle rateincreases as the cycle time increases. From this result, it isconsidered that thermal decomposition of DCS occurs and the siliconnitride film is formed by a CVD reaction.

FIG. 8 is a diagram showing the leakage current characteristics of thesilicon nitride film, and shows the electric field strength dependencyof the current density when an electric field is applied to the siliconnitride film. In FIG. 8, the horizontal axis represents the electricfield intensity Eg [MV/cm] and the vertical axis represents the currentdensity Jg [A/cm²]. The electric field intensity refers to the intensityof an electric field applied in the film thickness direction of thesilicon nitride film. The current density refers to a current per 1 cm²flowing when an electric field is applied in the film thicknessdirection of the silicon nitride film. In FIG. 8, the Jg-Egcharacteristics of the silicon nitride film (Example) in the case ofusing TrCS as the silicon-containing gas are indicated by acharacteristic line α, and the Jg-Eg characteristics of the siliconnitride film (Comparative Example) in the case of using DCS as thesilicon-containing gas are indicated by a characteristic line β. Inaddition, the Jg-Eg characteristics of the silicon nitride film formedby the CVD method (wafer temperature: 770 degrees C.) using a batch typeheat treatment apparatus are indicated by a characteristic line γ.

As shown in FIG. 8, when TrCS indicated by the characteristic line α isused, the current density Jg is reduced as compared with the case whereDCS indicated by the characteristic line β is used. Specifically, thecurrent density Jg when an electric field of 3 [MV/cm] is applied to thesilicon nitride film formed using TrCS indicated by the characteristicline α is 1.7×10⁻⁶ [A/cm²]. In contrast, the current density Jg when anelectric field of 3 [MV/cm] is applied to the silicon nitride filmformed using DCS indicated by the characteristic line β is 1.0×10⁻³[A/cm²]. In other words, the silicon nitride film formed using TrCS issmaller in leakage current and more excellent in insulation propertythan the silicon nitride film formed using DCS. In addition, the currentdensity is lower than the current density Jg available when an electricfield of 3 [MV/cm] is applied to the silicon nitride film formed by aCVD method using a batch type heat treatment apparatus.

FIG. 9 is a diagram showing the relationship between the temperature ofthe wafer and the loading effect. In FIG. 9, the horizontal axisrepresents the wafer temperature [degrees C.] and the vertical axisrepresents the loading effect [%]. The loading effect in FIG. 9 refersto the ratio of the film thickness of the silicon nitride film formed onthe surface of a wafer (patterned wafer) having an uneven pattern on thesurface thereof to the film thickness of the silicon nitride film formedon the surface of a bare (mirror surface) wafer. In FIG. 9, the resultobtained in the case of using TrCS as the silicon-containing gas isindicated by circular marks, and the result obtained in the case ofusing DCS is indicated by triangular marks.

As shown in FIG. 9, the loading effect when the wafer temperature is 760degrees C. and the silicon-containing gas is TrCS is about 10%, whereasthe loading effect when the wafer temperature is 760 degrees C. and thesilicon-containing gas is DCS is about 30%. That is to say, by usingTrCS as the silicon-containing gas, it is possible to suppress theloading effect at a high temperature (for example, 760 degrees C.).

In the above-described embodiment, the vacuum container 1 is an exampleof a processing chamber. In addition, the reaction gas nozzle 31 is anexample of a first processing gas supply part, and the reaction gasnozzle 32 is an example of a second processing gas supply part.Furthermore, the separation region D is an example of an inert gassupply region, and the nitriding step is an example of a reaction step.

Second Embodiment

In the second embodiment, as another example of the method of forming asilicon nitride film of the present disclosure, a case where a siliconnitride film is formed by using a batch type film forming apparatus thatperforms a film forming process in units of one batch constituted by alarge number of wafers mounted on a wafer boat will be described as anexample.

Film Forming Apparatus

First, a film forming apparatus suitable for carrying out the method offorming a silicon nitride film according to the embodiment of thepresent disclosure will be described. FIGS. 10 and 11 are schematicviews of another example of the film forming apparatus suitable forcarrying out the method of forming a silicon nitride film according tothe embodiment of the present disclosure. FIG. 10 shows a vertical crosssection of the film forming apparatus, and FIG. 11 shows a horizontalcross section of the film forming apparatus.

As shown in FIG. 10, the film forming apparatus of the second embodimentincludes a cylindrical processing container 210 having a ceiling and anopen lower end. The processing container 210 is an example of aprocessing chamber. The processing container 210 is made of quartz, forexample. The ceiling side of the processing container 210 is sealed by aquartz-made top plate 212. A flange portion 214 is provided in theopening at the lower end of the processing container 210. A stainlesssteel manifold may be provided at the lower end of the processingcontainer 210.

In the opening at the lower end of the processing container 210, a waferboat 220, which is a substrate holder for substantially horizontallyholding a plurality of wafers W at predetermined intervals in thevertical direction, is loaded and unloaded.

As shown in FIG. 11, the wafer boat 220 includes, for example, threesupport columns 222. The wafer boat 220 substantially horizontally holdsa plurality of (for example, 125) wafers W at predetermined intervalswhile supporting the outer edge portions of the wafers W. The wafer boat220 is placed on a table 226 via a quartz-made heat insulating cylinder224. The table 226 is supported by a rotating shaft 232 that penetratesa lid 230 made of stainless steel. When the wafer boat 220 is loadedinto the processing container 210 through the opening of the processingcontainer 210 and raised to a predetermined height position, the openingis airtightly closed by the lid 230.

At a position where the rotating shaft 232 penetrates the lid 230, thereis provided a bearing portion 234 provided with, for example, a magneticfluid seal and configured to rotatably hold the rotating shaft 232 whilemaintaining airtightness of the interior of the processing container210. For example, an O ring is interposed between the peripheral portionof the lid 230 and the flange portion 214 of the processing container210 to keep airtightness of the interior of the processing container210.

The rotating shaft 232 is attached to the tip of an arm 236 supported byan elevating mechanism (not shown) such as, for example, a boatelevator. The elevating mechanism can raise and lower the wafer boat220, the lid 230 and the like as a unit and can load and unload theminto and from the processing container 210.

A plasma generating mechanism 240 is provided on a part of the side wallof the processing container 210. The plasma generating mechanism 240 isformed by airtightly joining, for example, a quartz-made partition wall218 having a recessed cross-sectional shape, to the outer wall of theprocessing container 210 so as to cover a vertically elongated opening216 formed in the side wall of the processing container 210. The opening216 is formed to be elongated in the vertical direction so as to coverall the wafers W supported by the wafer boat 220.

A pair of plasma electrodes 242 facing each other is provided on theouter side surfaces of both side walls of the partition wall 218 alongthe length direction thereof (the vertical direction). A high-frequencypower source 246 for plasma generation is connected to the plasmaelectrodes 242 via a power supply line 244. By applying a high-frequencyvoltage of, for example, 13.56 MHz to the plasma electrodes 242, plasmacan be generated. Furthermore, for example, an insulating protectivecover 248 made of quartz is attached to the outside of the partitionwall 218 so as to cover the partition wall 218.

A gas supply pipe 250 for supplying a silicon-containing gas is insertedinto the lower part of the processing container 210. For example, twogas nozzles 252 are provided at the tip portion of the gas supply pipe250 so as to extend upward in the processing container 210. The gasnozzles 252 are made of a quartz tube and are disposed on both sides ofthe opening 216 of the plasma generating mechanism 240 so as to sandwichthe opening 216 as shown in FIG. 11. In the gas nozzles 252, a pluralityof gas discharge holes 254 is formed at predetermined intervals alongthe length direction thereof. The base end side of the gas supply pipe250 is connected to a silicon-containing gas supply source 256. A massflow controller 257, a valve 258 and the like are installed in the gassupply pipe 250.

In addition, a gas supply pipe 260 for supplying a nitrogen-containinggas is inserted into the lower part of the processing container 210. Atthe tip of the gas supply pipe 260, a gas nozzle 262 made of a quartztube is provided. As shown in FIGS. 10 and 11, the gas nozzle 262extends upward within the processing container 210. The gas nozzle 262is bent in the middle thereof and is disposed in the plasma generatingmechanism 240. In addition, a plurality of gas discharge holes 264 isformed in the gas nozzle 262 at predetermined intervals along the lengthdirection thereof. The base end side of the gas supply pipe 260 isconnected to a nitrogen-containing gas supply source 266. A mass flowcontroller 267, a valve 268 and the like are installed in the gas supplypipe 260.

A straight tubular quartz-made gas supply pipe 270 for supplying aninert gas is inserted into the lower part of the processing container210. The base end portion of the gas supply pipe 270 is connected to aninert gas supply source 276. A mass flow controller 277, a valve 278 andthe like are installed in the gas supply pipe 270.

In FIG. 10, for the convenience of illustration, the gas nozzles 252,the gas nozzle 262 and the gas supply pipe 270 are shown to be insertedinto the processing container 210 through the side wall on the lowerside of the processing container 210. However, in reality, they areinserted through the flange portion 214.

Around the processing container 210, a cylindrical heater 280 isprovided so as to surround the side circumferential surface of theprocessing container 210 from the outside. The heater 280 is configuredto heat the wafers W in the processing container 210 to a predeterminedtemperature (for example, 400 degrees C. to 850 degrees C.).

An exhaust port 219 is formed on the side wall surface on the lower sideof the processing container 210. An exhaust part 290 is provided in theexhaust port 219. The exhaust part 290 includes an exhaust passage 292connected to the exhaust port 219. A pressure regulation valve 294 andan exhaust device 296 such as a vacuum pump or the like are sequentiallyinstalled in the exhaust passage 292 to evacuate the inside of theprocessing container 210 to vacuum.

As shown in FIG. 10, the film forming apparatus includes a control part300. The control part 300 is composed of a computer having a CPU (notshown) and a memory part (not shown). A program incorporating a group ofsteps relating to the operation of the method of forming a siliconnitride film to be described later is recorded in the memory part. Theprogram is stored in a storage medium and installed in the computer fromthe storage medium.

Method of Forming Silicon Nitride Film

Next, a method of forming a silicon nitride film according to a secondembodiment will be described. As in the first embodiment, the method offorming a silicon nitride film according to the second embodiment is amethod of forming a silicon nitride film on the surface of the wafer Wby using an ALD (Atomic Layer Deposition) method in which an adsorptionstep and a nitriding step are repeated. The adsorption step is a step inwhich a silicon-containing gas (raw material gas) represented by ageneral formula XSiCl₃ (wherein X is an element whose bonding energywith Si is smaller than that of a Si—Cl bond) is supplied into a vacuumcontainer accommodating the wafer W to cause the silicon-containing gasto be adsorbed to the surface of the wafer W. As the silicon-containinggas, any gas may be used as long as it is represented by the generalformula XSiCl₃ (wherein X is an element whose bonding energy with Si issmaller than that of a Si—Cl bond). Examples of the silicon-containinggas include trichlorosilane (HSiCl₃), BrSiCl₃ and ISiCl₃. The nitridingstep is a step in which a nitrogen-containing gas (reaction gas) issupplied into the vacuum container to deposit an atomic layer or amolecular layer of a reaction product of the silicon-containing gas andthe nitrogen-containing gas.

Hereinafter, a case of using the above-described film forming apparatuswill be described as an example with reference to FIG. 12. The method offorming a silicon nitride film according to the second embodiment may becarried out using another film forming apparatus. FIG. 12 is a diagramfor explaining the method of forming a silicon nitride film according tothe second embodiment.

As shown in FIG. 12, in the method of forming a silicon nitride film, asilicon nitride film having a desired thickness is formed by repeating,plural times, a cycle composed of a purging step, an adsorption step, apurging step and a nitriding step. In the adsorption step, asilicon-containing gas represented by a general formula XSiCl₃ (whereinX is an element whose bonding energy with Si is smaller than that of aSi—Cl bond) is supplied from the gas nozzle 252 (FIG. 10). In thenitriding step, a nitrogen-containing gas (for example, NH₃) is suppliedfrom the gas nozzle 262 (FIG. 10). In the purging step, an inert gas(for example, N₂) is supplied from the gas supply pipe 270 (FIG. 10).

As described above, in the method of forming a silicon nitride filmaccording to the second embodiment, in the adsorption step, thesilicon-containing gas represented by the general formula XSiCl₃(wherein X is an element whose bonding energy with Si is smaller thanthat of a Si—Cl bond) is supplied to cause the silicon-containing gas tobe adsorbed to the surface of the wafer W. Accordingly, when theSi-containing gas is adsorbed to the surface of the wafer W, a Si—X bondis broken because the Si—X bond in XSiCl₃ is weaker than a Si—Cl bond.That is to say, three functional groups become chloro groups (Cl—).Therefore, the surface to which the silicon-containing gas is adsorbedhas a structure in which the electron density on a silicon atom (Si)decreases and the silicon atom (Si) is likely to make a bond with anitrogen atom (N) in an electrophilic manner. Thus, the surface iseasily nitrided by the nitrogen-containing gas such as NH₃ or the like.As a result, in the nitriding step performed after the adsorption step,the reaction rate of the silicon-containing gas and thenitrogen-containing gas is improved and the productivity is enhanced. Inaddition, the three-dimensional structure of SiN is easily formed.Therefore, the film quality is improved.

In addition, the unreacted bonding sites on the surface of the wafer Ware reduced by increasing the adsorption rate and the nitriding rate.Therefore, the variation in deposition rate is reduced in the plane ofthe wafer W, whereby the in-plane uniformity is improved.

Furthermore, since the three-dimensional structure of SiN is easilyformed, the film grows like a tree. As a result, the reaction surface onwhich the adsorption of the silicon-containing gas and the nitriding ofthe silicon-containing gas are performed is enlarged. Thus, the time(incubation time) until the film begins to grow on the surface of thewafer W is shortened.

Next, an Example and a Comparative Example will be described. In theExample and the Comparative Example, silicon nitride films were formedunder the following process conditions. In addition, the characteristicsof the silicon nitride films formed in the Example and the ComparativeExample were evaluated.

Example

-   -   Silicon-containing gas: TrCS    -   Nitrogen-containing gas: NH₃    -   Wafer temperature: 700 degrees C., 750 degrees C., and 800        degrees C.

Comparative Example

-   -   Silicon-containing gas: DCS    -   Nitrogen-containing gas: NH₃    -   Wafer temperature: 640 degrees C., 660 degrees C., and 700        degrees C.

FIG. 13 is a diagram showing the relationship between the wafertemperature and the cycle rate of the silicon nitride film. In FIG. 13,the horizontal axis represents the wafer temperature [degrees C.] andthe vertical axis represents the cycle rate [Å/cycle]. Furthermore, inFIG. 13, the cycle rate of the silicon nitride film (Example) in thecase of using TrCS as the silicon-containing gas is indicated bycircular marks, and the cycle rate of the silicon nitride film(Comparative Example) in the case of using DCS as the silicon-containinggas is indicated by triangular marks.

As shown in FIG. 13, when TrCS is used, even if the wafer is heated to800 degrees C., the cycle rate is hardly changed. From this result, itis considered that even if the wafer is heated to 800 degrees C., theTrCS is not thermally decomposed and the silicon nitride film is formedby the deposition of each atomic layer attributable to an ALD reaction.On the other hand, in the case of using DCS, when the wafer temperatureis 640 degrees C., the same cycle rate as in the case of TrCS isobtained. However, as the wafer temperature increases, the cycle ratebecomes high. From this result, it is considered that when thetemperature of the wafer is higher than 640 degrees C., thermaldecomposition of DCS occurs and a silicon nitride film is formed by aCVD reaction.

FIG. 14 is a diagram showing the relationship between the wafertemperature and the in-plane uniformity of the film thickness of thesilicon nitride film. In FIG. 14, the horizontal axis represents thewafer temperature [degrees C.] and the vertical axis represents thein-plane uniformity (±%) of the film thickness of the silicon nitridefilm. In FIG. 14, the in-plane distribution of a convex shape having alarge film thickness at the central portion of the wafer and a smallfilm thickness at the outer peripheral portion is shown as a positivevalue, and the in-plane distribution of a concave shape having a smallfilm thickness at the central portion of the wafer and a large filmthickness at the outer peripheral portion is shown as a negative value.In FIG. 14, the in-plane uniformity of the film thickness of the siliconnitride film (Example) in the case of using TrCS as thesilicon-containing gas is indicated by circular marks, and the in-planeuniformity of the film thickness of the silicon nitride film(Comparative Example) in the case of using DCS as the silicon-containinggas is indicated by triangular marks. In addition, the black marksindicate the results obtained when the silicon nitride film was formedon the surface of a bare (mirror surface) wafer, and the white marksindicate the results obtained when the silicon nitride film was formedon the surface of the wafer on which a concavo-convex pattern having asurface area of forty times is formed.

As shown in FIG. 14, it was confirmed that in the case of using TrCS,regardless of whether the wafer temperature is 750 degrees C. or 800degrees C., good in-plane uniformity of ±1% or less is obtainedirrespective of the surface area of the wafer. On the other hand, it wasconfirmed that in the case of using DCS, regardless of whether the wafertemperature is 640 degrees C. or 700 degrees C., the deposition amountof the silicon nitride film in the wafer plane varies depending on thesurface area of the wafer. From this result, it is considered that byusing TrCS, as compared with the case of using DCS, it is possible tosuppress the so-called loading effect in which the deposition amount inthe wafer plane fluctuates depending on the surface area on the wafer.

FIG. 15 is a diagram showing the relationship between the wafertemperature and the incubation cycle. In FIG. 15, the horizontal axisrepresents the wafer temperature [degrees C.] and the vertical axisrepresents the incubation cycle [cycle]. In FIG. 15, the incubation timein the case of using TrCS as the silicon-containing gas is indicated bycircular marks, and the incubation time in the case of using DCS as thesilicon-containing gas is indicated by triangular marks.

As shown in FIG. 15, it was confirmed that by using TrCS, compared withthe case of using DCS, the incubation cycle (time) can be shortened toone half or less.

Adsorption Mechanism

Next, the mechanism of adsorbing the silicon-containing gas in themethod of forming a silicon nitride film according to the embodiments ofthe present disclosure will be described by taking as an example thecase of using SiHCl₃ as the silicon-containing gas.

FIG. 16 is a diagram for explaining the bonding energy. As shown in FIG.16, the bonding energies of a Si—Si bond, a Si—H bond, and a Si—Cl bondare 222 kJ/mol, 299 kJ/mol, and 406 kJ/mol, respectively. The Si—H bondis thermally decomposed in a temperature range of 400 degrees C. to 500degrees C. or higher to release a hydrogen atom (H). In addition, theSi—Cl bond is thermally decomposed in a temperature range of 800 degreesC. to 850 degrees C. or higher to release a chlorine atom (Cl).

FIGS. 17A and 17B are diagrams for explaining the adsorption mechanismof the silicon-containing gas. FIG. 17A shows the adsorption mechanismwhen SiH₂Cl₂ (DCS) is used as the silicon-containing gas, and FIG. 17Bshows the adsorption mechanism when SiHCl₃ (TrCS) is used as thesilicon-containing gas.

As shown in FIG. 17A, in SiH₂Cl₂, when the wafer is heated to atemperature range (400 degrees C. to 500 degrees C. or higher) where ahydrogen atom (H) is released from a Si—H bond, two hydrogen atoms (H)are released and two dangling bonds are generated. At this time, onedangling bond is bonded and adsorbed to a nitrogen atom (N) on thesurface of the wafer, and the other dangling bond is bonded to anotherSiH₂Cl₂ molecule. That is to say, excessive adsorption in which multiplelayers of silicon are adsorbed during one cycle may occur.

On the other hand, as shown in FIG. 17B, in SiHCl₃, when the wafer isheated to a temperature range (for example, 400 degrees C. to 500degrees C. or higher) in which a hydrogen atom (H) is released from aSi—H bond and to a temperature range (800 degrees C. to 850 degrees C.or lower) in which a chlorine atom (Cl) is not released from a Si—Clbond, one hydrogen atom (H) is released and one dangling bond isgenerated. At this time, the dangling bond is bonded and adsorbed to anitrogen atom (N) on the surface of the wafer. Since there is no otherdangling bond, even if another SiHCl₃ reaches the surface to whichSiHCl₃ is adsorbed, a new adsorption reaction does not proceed. That isto say, it is possible to prevent the occurrence of excessive adsorptionin which multiple layers of silicon are adsorbed during one cycle. As aresult, ideal ALD film formation can be realized, and a silicon nitridefilm with high quality and good in-plane uniformity can be formed. Inview of the foregoing, in the adsorption step, the wafer is preferablyheated to 400 degrees C. to 850 degrees C., more preferably 500 degreesC. to 800 degrees C.

Application Example of Silicon Nitride Film

An application example of the silicon nitride film according to theembodiments of the present disclosure will be described. The siliconnitride film according to the embodiments of the present disclosure maybe suitably used as a charge storage layer (charge trap layer) for usein a three-dimensional NAND flash memory of a Si—SiO₂—SiN—SiO₂—Sistructure (hereinafter referred to as “SONOS structure”).

FIG. 18 is a diagram showing an example of a three-dimensional NANDflash memory with a SONOS structure. As shown in FIG. 18, thethree-dimensional NAND flash memory with a SONOS structure includes astacked body 510 and a columnar body 520.

The stacked body 510 is formed by alternately stacking silicon layers512 and silicon oxide films 514. A through-hole 516 penetrating in thestacking direction of the stacked body 510 is formed in the stacked body510. The columnar body 520 is formed inside the through-hole 516. InFIG. 18, a part of the through-hole 516 is shown.

The columnar body 520 includes a columnar insulator 522, a channel layer524, a tunnel insulating film 526, a charge storage layer 528, and ablock insulating film 530.

The columnar insulator 522 is formed at the center of the columnar body520. The columnar insulator 522 is formed of, for example, a siliconoxide film.

The channel layer 524 is formed between the outer surface of thecolumnar insulator 522 and the inner surface of the through-hole 516.The channel layer 524 is formed of a semiconductor such as, for example,silicon.

The tunnel insulating film 526 is formed between the inner surface ofthe through-hole 516 and the channel layer 524. The tunnel insulatingfilm 526 is formed of, for example, a silicon oxide film.

The charge storage layer 528 is formed between the inner surface of thethrough-hole 516 and the tunnel insulating film 526. The charge storagelayer 528 is formed of, for example, a silicon nitride film. If thecharge storage layer 528 is formed of a silicon nitride film, it ispreferable because the charge trapping sites in the film are increased.In addition, if the charge storage layer 528 is formed of a siliconnitride film, it is preferable because a high band barrier can be formedwith respect to the silicon oxide film constituting the tunnelinsulating film 526 and the block insulating film 530.

The block insulating film 530 is formed between the inner surface of thethrough-hole 516 and the charge storage layer 528. The block insulatingfilm 530 is formed of, for example, a silicon oxide film.

Incidentally, a silicon nitride film with high quality and good in-planeuniformity is required for the charge storage layer 528 for use in athree-dimensional NAND flash memory with a SONOS structure. In addition,as the surface area increases due to pattern miniaturization, a siliconnitride film with a small loading effect is required.

As a method of forming a high-quality silicon nitride film, filmformation by an ALD method at a high temperature (for example, 700degrees C. or higher) is effective. However, silicon-containing gasessuch as Si₂HCl₂ (DCS) and Si₂H₆ (HCD) which have been conventionallyused as raw material gases are autolyzed under a high temperature tocause excessive adsorption of Si. This makes it impossible to obtaingood in-plane uniformity.

In contrast, in the method of forming a silicon nitride film accordingto the embodiments of the present disclosure, SiHCl₃ (TrCS) is used as araw material gas. Thus, the dangling bond at the time of Si adsorptionis limited to one. This makes it possible to prevent excessiveadsorption and physical adsorption of Si. As a result, it is possible torealize ideal ALD film formation and to form a silicon nitride film withhigh quality and good in-plane uniformity.

While a mode for carrying out the present disclosure has been describedabove, the above descriptions do not limit the contents of the presentdisclosure. Various modifications and improvements may be made withinthe scope of the present disclosure.

In the above-described embodiments, a semiconductor wafer has beendescribed as an example of a substrate. However, the present disclosureis not limited thereto. The present disclosure may also be applied to aglass substrate, an LCD substrate, a ceramic substrate, or the like.

In the above-described embodiments, the semi-batch type and batch typefilm forming apparatuses have been described as examples. However, thepresent disclosure is not limited thereto. It may be possible to use,for example, a single-wafer type film forming apparatus that performs afilm forming process one by one.

In the above-described embodiments, a case where a silicon nitride filmis formed as an example of a silicon-containing film has been describedas an example. However, the present disclosure is not limited thereto.For example, the present disclosure may be applied to a case of forminga silicon oxide film or a silicon oxynitride film. In the case offorming a silicon oxide film, an oxygen-containing gas such as oxygen orozone may be used as a reaction gas instead of the nitrogen-containinggas. In the case of forming a silicon oxynitride film, anitrogen-containing gas and an oxygen-containing gas may be used asreaction gases.

According to the method of forming a silicon-containing film disclosedherein, it is possible to achieve both the enhancement in productivityand the improvement in film quality.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the disclosures. Indeed, the embodiments described herein maybe embodied in a variety of other forms. Furthermore, various omissions,substitutions and changes in the form of the embodiments describedherein may be made without departing from the spirit of the disclosures.The accompanying claims and their equivalents are intended to cover suchforms or modifications as would fall within the scope and spirit of thedisclosures.

What is claimed is:
 1. A method of forming a silicon-containing film,comprising: an adsorption step of supplying a silicon-containing gasrepresented by a general formula XSiCl₃ (wherein X is an element whosebonding energy with Si is smaller than bonding energy of a Si—Cl bond)into a processing chamber accommodating substrates to cause thesilicon-containing gas to be adsorbed to a surface of each of thesubstrates; and a nitriding step of nitriding the silicon-containing gasadsorbed to the surface of each of the substrates to form a siliconnitride by supplying a nitriding gas, which nitrides thesilicon-containing gas, to the surface of each of the substrate anddepositing a reaction product of the silicon-containing gas and thenitriding gas on the surface of each of the substrate.
 2. The method ofclaim 1, wherein in the adsorption step, the substrates are heated to atemperature of 400 degrees C. to 850 degrees C.
 3. The method of claim1, wherein the silicon-containing gas is one of HSiCl₃, BrSiCl₃ andISiCl₃.
 4. The method of claim 1, wherein the silicon-containing gas isHSiCl₃.
 5. The method of claim 1, wherein the nitriding gas is anitrogen-containing gas.
 6. The method of claim 5, wherein the nitridinggas is NH₃.
 7. The method of claim 1, wherein a recess is formed on thesurface of each of the substrates, and the silicon-containing film isformed in the recess.